1. Field of the Invention
The present invention relates to a lumbar support suitably used for a cushion for a seat, which is used by being mounted in a seat structure for transportation machines such as an automobile, a plane, a train, a ship, a fork lift and the like, those seat cushion and a seat back, a cushion for a seat, into which the lumbar support is incorporated, and a seat structure into which the lumbar support is incorporated.
2. Description of the Related Art
In Patent Document 1, a back mat which is made by attaching a bag as an air cushion on a flat rubber mat base is disclosed. The back mat is used by fixing on a seat back of an office chair, a car seat, and the like with a belt member. It is also disclosed that the air cushion is provided at a position corresponding to the vicinity of a seated person's waist, and formation of an air cushion in a plurality of rooms to ensure air permeability. In Patent Document 2, disclosed is a lumbago protection seat cover formed in an integral structure provided with a bottom cushion and a back cushion, attached with an air cushion at a position corresponding to the vicinity of the waist in the back cushion, without description of a base material. In Patent Document 3, disclosed is a seat cover provided with a lumbar support which can adjust a position of a pad loaded in a belt body folded into two by adjusting the position to fix the belt body.
[Patent Document 1] Japanese Utility Model Registration No. 3057132
[Patent Document 2] Japanese Utility Model Application No. Hei 6-82969
[Patent Document 3] Japanese Patent Application Laid-open No. 2002-325651
The air cushions disclosed in Patent Documents 1 and 2 use a soft flexible material as a bag to be filled with air, a pump is connected to this bag via a connection tube and air is loaded therein. However, no matter how airtight the bag and the connection tube, air still leaks gradually during use. Therefore, the desired elasticity of the air cushion is difficult to obtain depending on the air leaked amount, and the cushion's function as a sufficient lumbar support to support the waist disappears at an early stage, resulting in an increase in the number of times the cushion needs to be refilled by pump. Especially, on a driver's seat in a car, if the air cushion comes short of elasticity due to air leakage, it is extremely difficult to adjust the pump during driving. It is possible to adjust a feeling of support to the waist to suit individual preferences with the technology described in Patent Document 3, but this only goes as far as changing the height of the pad by adjusting a position to fix the belt body using a Hook-and-Loop fastener. In other words, since it is only a structure to be able to adjust the height of a lumbar support, it is impossible to adjust a feeling of cushioning unlike an air cushion type lumbar support disclosed in the Patent Document 1, and the like.
All of the Patent Documents 1 to 3 disclose a lumbar support having a plurality of bulging portions. This is mainly for ensuring air permeability by gaps between the bulging portions. However, if curvature of the bulging portion is too small or too large, a feeling of a strong pressure contact or a sense of a lack of conformity is felt when coming into contact with the back (the waist). That is, a lumbar support is provided to support in the vicinity of the third to fourth human lumbar vertebrae, and the average distance between the third and fourth lumbar vertebrae of Japanese adults is about 40 mm. When the curvature of a touched surface is too small, a nervous system between the third lumbar vertebra and the fourth lumbar vertebra is pressed, and when it is too large, a sense of lack of conformity or an unpleasant feeling is felt because it is not parallel to a curve of the spinal column.